1. Field of the Invention
The present invention relates to a clothes dryer and, more particularly, to a method for controlling a clothes dryer.
2. Description of the Background Art
In general, in a clothes dryer, an internal drum is rotated to rotate clothes in a drum, heat is generated by a heater, and at this time, low temperature little moisture air passes the heater to be changed to high temperature little moisture air according to rotation of a drying fan.
The clothes dryer heats the clothes by introducing the high temperature little moisture air into the drum. The high temperature little moisture air is changed to high temperature much moisture air by steam generated as the clothes are heated, and the high temperature much moisture air is condensed by an internal condenser to turn to a low temperature little moisture air with its moisture removed, and then, as the low temperature little moisture air passes the heater according to rotation of the drying fan, it is changed to high temperature little moisture air.
In other words, the clothes dryer dries clothes by repeatedly performing the process of introducing air into the drum and heating clothes.
When drying of the clothes is completed, the heater is stopped and only the motor is driven to cool clothes so that a user can easily draw clothes out from the drum.
In order to accurately dry clothes in the drum of the clothes dryer, the clothes dry completion point in the drum should be precisely detected. If the clothes dry completion point is not accurately detected, clothes can be damaged due to overdry or a fire can be broken out. Or, the clothes dry operation can be finished with clothes not fully dried yet due to underdry. Thus, the clothes dry completion point of the clothes dryer must be precisely detected.
In brief, in the conventional clothes dryer, clothes are dried in the drum, and a clothes dry completion point is detected on the basis of a change in a temperature of air discharged from the drum and a change in a temperature of air before being heated by the heater after being condensed in the condenser.
The operation of the conventional clothes dryer will be described with reference to FIG. 1 as follows.
FIG. 1 is a graph showing a change in a temperature of air discharged from an exit of the drum and a change in a temperature of an entrance of the heater before being heated by the heater after being discharged from the drum and condensed in the condenser in drying clothes in accordance with the conventional art.
As shown in FIG. 1, during a preheat-drying period, an initial drying period in drying clothes, thermal energy generated from the heater increases air, clothes and an ambient temperature so that moisture at the surface of clothes can be easily evaporated. During a constant rate period of drying where drying proceeds in full-scale, thermal energy is sued for evaporating moisture at the surface of clothes, so that a temperature distribution shows that a temperature of the circulated air is maintained constantly without a big change.
During a falling rate period of drying at a later part of drying, there is little moisture in clothes and thus most thermal energy is used to increase a temperature of a cycle air itself, so that a temperature of the cycle air which has passed the drum is sharply increased.
In addition, since there is little moisture in the cycle air, condensing does not occur at the condenser and heat of condensation is not generated, and a temperature of the entrance of the heater after passing through the condenser is rather reduced. Namely, in the conventional clothes dryer, a dry completion point is determined on the basis of the change in the temperature of the exit of the drum and the change in the temperature of the entrance of the heater. For example, the cycle air temperature at the exit of the drum and the cycle air temperature at the entrance of the heater are detected, and then, if a detected temperature difference between the two cycle airs is not smaller than a predetermined temperature, it is determined that drying of clothes has been completed.
However, the conventional clothes dryer cannot precisely detect the clothes dry completion point with the temperature difference between two cycle airs, causing a problem that clothes can be overdried beyond it needs or clothes is underdried that a clothes drying operation is stopped even though clothes is not completely dried.
In addition, even after the point at which drying is completed, the heater is continuously heated only to increase the temperature of the cycle air itself, causing a problem that power is much wasted unnecessarily.
U.S. Pat. No. 6,449,876 issued Sep. 17, 2002 discloses detailed descriptions on the conventional clothes dryer.